virtual int i ()=0Returns the row index. virtual int j ()=0Returns the column index. virtual void set (double val)=0Set the current element to val. virtual void accum (double val)Add val to the current element. virtual double get ()=0Return the value of the current element. virtual operator int ()=0Return nonzero if there are more elements. virtual void operator++ ()=0Move to the next element. void operator++ (int)virtual void reset ()=0Start the iteration over.